1. Field of the Invention
The present invention relates to a twisted flat cable used for internal wiring of electronic equipment such as computers.
2. Prior Art
A flat cable used for internal wiring of electronic equipment such as computers is prepared in such that conductors are arranged in parallel to each other, and they are insulated in accordance with a trend of downsizing as well as weight reduction for electronic equipment for the purpose of cut-back for wiring such as space-saving wiring or of cut-back for mounting a flat cable, and maintenance and inspecting operations therefor.
Merits of such flat cable as mentioned above are enumerated in the following items (1) to (6).
(1) It is possible to omit bundling insulated wire cores.
(2) It is possible to elevate a packaging density of electronic parts or the like.
(3) There is little fear of erroneous wiring, besides maintenance and inspection are also easy.
(4) There is sufficient flexibility so that wiring is easy.
(5) It is possible to reduce the number of steps for terminal processing.
(6) It is easy to correspond to automation for cutting a cable or mounting a connector.
In FIGS. 1, 2 and 3, a twisted flat cable being a type of flat cables are shown, respectively, wherein FIG. 1 is a plan view showing a conventional twisted flat cable; FIG. 2 is a sectional view taken along the line Axe2x80x94A of the twisted flat cable shown in FIG. 1; and FIG. 3 is a plan view showing a plastic tape used in the twisted flat cable shown in FIG. 1.
A twisted flat cable 51 shown in FIG. 1 is composed of a plurality of insulated wire cores 52 arranged in parallel to each other wherein molten sections 53 each prepared by melting all the adjacent insulated wire cores 52 with each other are alternately disposed in the longitudinal direction thereof with a predetermined interval with respect to pair-twisted sections 54 each prepared by pair-twisting each adjacent pairs of insulated wire cores among adjacent insulated wire cores 52 with each other.
A plastic tape 55 is welded (laminated) on either surface (the under surface in FIG. 2) of the arranged insulated wire cores 52 over the whole length thereof. An adhesive layer has been prepared on either surface of the plastic tape 55 (the upper surface in FIG. 2). Lamination is made after bonding the insulated wire cores 52 to the adhesive layer.
In the above-mentioned twisted flat cable 51, however, since the plastic tape 55 has been disposed over the whole length of the twisted flat cable, the plastic tape 55 does not enter flexibly into a gap defined in between pair-twisted sections 54, so that there is such a tendency that the pair-twisted sections 54 are collapsed in a laminating step. Furthermore, since the plastic tape 55 has been applied to the whole surface of the twisted flat cable 51, there has been such a tendency that dielectric constant thereof becomes higher between insulated wire cores than that of a product without lamination processing.
Thus, there has been such a problem that impedance decreases in a pair each of the molten sections and the pair-twisted sections 54.
Accordingly, an object of the present invention is to solve the above-described problems, and to provide a twisted flat cable, which exhibits flexibility and accompanies with no decrease of impedance in laminating step.
In order to achieve the above-described object, a twisted flat cable of the present invention composed of a plurality of insulated wire cores arranged in parallel to each other wherein molten sections each prepared by melting all the adjacent insulated wire cores with each other are alternately disposed in the longitudinal direction thereof with respect to pair-twisted sections each prepared by pair-twisting each adjacent pairs of insulated wire cores among adjacent insulated wire cores with each other, comprises a plastic tape having an adhesive layer on either surface thereof as well as having a plurality of perforations defined thereon being laminated on the insulated wire cores arranged in parallel to each other so as to be in contact with the adhesive layer.
According to the present invention, a plurality of perforations has been defined on a plastic tape to be laminated on insulated wire cores. Accordingly, intrusions of the plastic tape in between each of pair-twisted sections are elevated in laminating step of the plastic tape. As a result, collapses in pair-twisted sections decrease, and in addition, portions of a tape material corresponding to perforations defined on the plastic tape are replaced by air, so that dielectric constant between conductors of the insulated wire cores decreases, whereby decrease in impedance can be reduced.